Axenic growth of Entamoeba histolytica in semi-defined TI-S-114 medium was enhanced by addition of nine amino acids, calcium, magnesium and glycogen. A low-density bovine lipoprotein containing cholesterol substituted for bovine serum in two undefined media used for axenic cultivation of this parasite. An in-depth study of Concanavalin A induced agglutination of E. histolytica showed agglutination to be modulated by temperature and composition of media, and was most pronounced during late log-phase growth. Con A agglutination could not be correlated with pathogenicity. Reversibility of the phenomenon is reported for the first time. A spontaneous, reversible agglutination of E. histolytica, not blocked by AlphaD-methylmannoside, a Con A inhibitor is reported. Quantitative kinetic studies of ligand induced surface receptor redistribution using FITC labeled Con A showed peak binding capacity occurred during mid-log-phase growth in a pathogenic strain of ameba, and during late log-phase growth of a non-pathogenic strain. Amebae, after internalizing surface bound Con A, were not susceptible to further Con A agglutination. Esterases have proved useful for isoenzyme separation of E. histolytica isolates belonging to a single pathogenic zymodeme (Classification of Sargeaunt). Giardia intestinalis infections were induced in both intact and immune deficient newborn mice via intragastric inoculation through the abdominal wall. Infections were self-limiting. Chronic infections could not be induced.